A conventional coated abrasive comprising a backing and an abrasive layer is prepared by (i) applying an adhesive resin on the backing to form a first adhesive layer (a make coat), (ii) sprinkling abrasive grains on the first adhesive layer, (iii) pre-drying, (iv) applying a second adhesive layer (a size coat) on the abrasives deposited on the first adhesive layer, and (v) drying.
Such conventional coated abrasive shown in FIG. 1 has problems in that (i) the abrasive grains deposited in the abrasive layer tend to fall off during use, and (ii) in case of grinding an alloy steel or a nonferrous metal article, the coated abrasive undergoes degradation brought about by the frictional heat. In order to solve these problems, U.S. Pat. Nos. 3,997,302 and 4,770,671 disclose a method of adding a grinding aid to the second adhesive layer, but the use life of the coated abrasive is not significantly improved.
Modified coated abrasives have been proposed as described below. FIG. 2 shows a coated abrasive comprising two abrasive layers, disclosed in Korean Patent No. 486,954. However, its flexibility is not satisfactory for use for grinding a curved surface: because a limited amount of filler can be used in the first adhesive layer, the first abrasive layer does not undergo even wearing during dry sanding. In addition, the improved cutting performance rate by about 20 to 30% is only marginal in light of the fact that the production cost thereof becomes 70 to 80% higher.
Korean Patent No. 398,942 discloses a method for forming three-dimensional structures containing abrasive grains as shown in FIG. 3, by applying a slurry containing abrasive grains on a backing using an intaglio knurling tool and drying the resulting sheet by UV radiation. However, the coated abrasive prepared by this method has much poorer early-stage cutting performance characteristics as compared with the conventional coated abrasive shown in FIG. 1. Further, in case of heavy duty sanding, the three-dimensional structures undergo rapid wearing and thus it is useful only for finishing.
Further, U.S. Pat. No. 4,364,746 discloses a method for preparing a coated abrasive by applying agglomerated minerals on an adhesive layer formed on a backing (FIG. 4). However, the coated abrasive prepared by this method has problems in that (i) the irregular form of the agglomerated minerals tends to create scratches on the work piece surface, and (ii) its manufacturing cost is high.